WO2011024337A1 - Digital-analog convertor and delta sigma type digital-analog conversion device - Google Patents

Abstract

Highly accurate DA conversion can be performed, and the increase in circuit scale and consumption current can be prevented, without decreasing the conversion accuracy due to variation in production. A ring-shaped resistive circuit (1) composed of resistive elements (R₁ to R_N) is provided, and a node of the ring-shaped resistive circuit (1) to which reference voltage terminals (V_ref1, V_ref2) are connected by connection circuits (2, 3), a node of the ring-shaped resistive circuit (1) connected to an analog signal output terminal (V_out) by a connection circuit (4), and a node of the ring-shaped resistive circuit (1) opened by an open circuit (5), are circulated at each AD conversion of a digital signal. In one of the circulation methods, at the time of present conversion, the state of the connection circuits (2, 3) which connect the two reference voltage terminals (V_ref1, V_ref2) with the resistive element group is set to the same state as the state of the connection circuit (4) which has been used for connecting the analog signal output terminal (V_out) with the resistive element group in the previous conversion. With respect to the open circuit (5) which connects the resistive elements is set to a state opposite to the state of the connection circuits (2, 3) which connect the two reference voltage terminals with the resistive element group.

Description

Digital-analog converter and delta-sigma type digital-analog converter

The present invention relates to a digital-analog converter (hereinafter referred to as a DA converter) that performs an operation for converting a digital signal into an analog signal, and a delta-sigma digital-analog converter (hereinafter referred to as a delta-sigma type) using the same. In particular, it relates to the reduction of resistance mismatch due to manufacturing variations.

There are various configurations of DA converters that convert digital signals into analog signals. As an example, a resistor string type DA converter as shown in FIG. 4 is generally known. This resistor string type DA converter has a number of resistor elements (resistor elements R ₁ , R ₂ ,..., R _N) between two reference voltage terminals V _ref1 and V _ref2 according to the required resolution. Are arranged in series. Each node between the resistance elements is connected to the analog signal output terminal V _out via the switches S ₁ , S ₂ ,..., S _N−1 . By selecting one of the switches S ₁ , S ₂ ,..., S _N-1 to be turned on according to the value of the input digital signal to be converted, the reference voltage terminals V _ref1 , V An analog output voltage obtained by dividing the voltage difference of _ref2 by (N−1) is obtained.

Features of the resistor string type DA converter include a small differential nonlinearity error, excellent monotonicity, and a large integral nonlinearity error due to manufacturing variations. A large integral nonlinearity error leads to worsening of distortion of the output waveform.

As another example, there is a resistance type DA converter as shown in FIG. This resistive DA converter has two reference voltage terminals V _ref1 and V _ref2 and a group of resistive elements having the same resistance value R (resistive elements R ₁ , R ₂ ,..., R according to the required resolution). to consist of _N), 1-bit DA performing selectively connected to control in accordance with a value of one and the converted digital signal of the resistance element group at one end and a reference voltage terminal V _ref1 and the reference voltage terminal V _ref2 converter DA _1, DA _2, ···, comprising a DA _N.

Now, certain input signals D ₁ , D ₂ ,..., _DN are inputted, and the 1-bit DA converters DA ₁ , DA ₂ ,..., DA _k output the voltage of the reference voltage terminal V _ref2 , 1-bit DA converter DA _k + 1, DA _k + 2, it is assumed ..., and DA _N has output voltage of the reference voltage terminal V _ref1. At this time, resistance elements R ₁ , R ₂ ,..., R _k are connected in parallel between the analog signal output terminal V _out and the reference voltage terminal V _ref1 , and the analog signal output terminal V _out and the reference voltage terminal V between _ref2 resistive element _{R k + 1, R k +} 2, ···, because R _N are connected in parallel, the analog signal output terminal V _out at two resistance values R / k, R / (N -K)
The voltage divided by is obtained.

In the resistive DA converter as shown in FIG. 5 described above, as a method for reducing the influence due to manufacturing variations, a method called Dynamic Element Matching (DEM) shown in Patent Document 1 is known. The DEM is a technique for improving distortion characteristics by circulating the output node of the DA converter, thereby randomizing mismatch due to manufacturing variation, that is, variation in the resistance value R.

In the resistance type DA converter, the resistor element group Assuming (resistive element R _1, R _2, · · ·, consists R _N) has a mismatch due to manufacturing variations, the voltage actually obtained is the Deviation from the desired voltage causes variations in the output signal. However, by using the DEM introduced earlier, k resistance elements are connected to the reference voltage terminal V _ref1 and (N−k) resistance elements are connected to the reference voltage terminal V _{ref2 as} in the previous example. In this case, k different resistance elements are connected to the reference voltage terminal V _ref1 every time conversion is performed, and similarly, different resistance elements (Nk) are connected to the reference voltage terminal V _ref2 , which is caused by manufacturing variations. Mismatches are randomized and distortion deterioration is reduced.

As described above, in the resistance type DA converter of FIG. 5, the use of DEM can reduce deterioration of distortion due to manufacturing variations. However, on the other hand, the resistance component of the reference voltage terminals V _ref1 and V _ref2 is connected in series to the two parallel resistance element groups used for the voltage division of the DA converter, and thus flows through the DA converter. There is another problem that the current value deviates from the ideal value and the distortion becomes worse.

For this problem, as disclosed in Patent Document 2, it is known that the deterioration of distortion can be reduced by using a current compensation circuit. In the current compensation circuit, a current compensation circuit having the same current characteristics as the DA converter is connected in parallel to a DA converter whose current value is data-dependent, and the current compensation circuit is operated in a phase opposite to that of the DA converter. This is a technique for keeping the total of the current values flowing constant. However, the problems with this method are that the circuit scale is approximately doubled and the current value flowing through the circuit is approximately doubled. In the resistor string type DA converter, since the flowing current is always constant, such a problem does not occur.

Incidentally, when high-speed conversion is not required, a delta-sigma type DA converter as shown in FIG. 6 is often used because low-power consumption and high-precision conversion can be easily realized. The delta sigma type DA converter includes a digital interpolation filter 10 that interpolates a digital input Din, a delta sigma modulator 20 that performs delta sigma modulation of a digital signal output from the digital interpolation filter 10, and a delta sigma modulator 20. This is constituted by a general DA converter 30 typified by the resistance type DA converter, which converts an output signal from digital to analog. An analog output Aout is output from the DA converter 30.

The digital interpolation filter 10 outputs a digital signal having a certain oversampling frequency f _os while preventing aliasing with respect to a certain sampling frequency f _s and an n-bit digital input signal DIN. The oversampling frequency f _os is between the sampling frequency f _s and the oversampling rate OSR.
f _os = OSR × f _s
Have a relationship. The oversampling frequency f _os, generally 64f _s, the frequency of such 128f _s used.

The delta sigma modulator 20 performs noise shaping on the digital signal obtained from the digital interpolation filter 10 and converts the digital signal into a lower resolution digital signal having a frequency higher than the sampling frequency f _s .

The DA converter 30 DA-converts the high-frequency, low-resolution digital signal obtained from the delta-sigma modulator 20, and outputs an analog signal.

As described above, highly accurate DA conversion can be performed by using a delta-sigma type DA converter. However, if the DA converter 30 in the delta sigma type DA converter has manufacturing variations or fluctuations in the current value depending on the digital data input, a conversion error occurs and the intended conversion accuracy cannot be obtained.

Therefore, the conversion accuracy is maintained by using the DEM and the current compensation circuit introduced earlier and adopting the configuration shown in FIG. In FIG. 7, reference numeral 40 denotes a DEM circuit, and reference numeral 50 denotes a DA converter with a current compensation circuit.

However, like the above resistance type DA converter, there is a trade-off in which the conversion accuracy is improved while the circuit scale and the current consumption are increased.

JP-A-7-99451 Japanese translation of PCT publication No. 2004-510381 Japanese Patent No. 3323460

The resistor string type DA converter shown in FIG. 4 has a small differential nonlinearity error, is excellent in monotonicity, and is a widely used circuit. However, when the resistance values of the resistance elements arranged in series vary due to the influence of manufacturing variations of the semiconductor integrated circuit, the output voltage deviates from a desired voltage due to mismatch of the resistance elements. As a result, there is a problem that the integral nonlinearity error of the DA converter becomes large and the distortion of the output signal deteriorates.

Further, it is known that if the resistance type DA converter shown in FIG. 5 is used, the influence of manufacturing variations can be reduced by using DEM. However, this resistive DA converter has another problem of distortion deterioration due to the data dependence of the current value. As a countermeasure for this problem, the insertion of a current compensation circuit is known. However, when this method is used, the circuit area and current consumption are approximately doubled.

Further, in the delta-sigma type DA converter shown in FIG. 6, the conversion accuracy is lowered due to manufacturing variations and current value fluctuations. As shown in FIG. 7, the influence can be reduced by inserting the DEM circuit and the current compensation circuit, but the circuit scale and current consumption increase.

Manufacturing variation in the semiconductor process is an unavoidable issue, and a design method that reduces the influence of manufacturing variation with a simpler structure is required to reduce the size and power consumption of the DA converter.

Accordingly, an object of the present invention is to provide a DA converter and a delta-sigma type DA converter that can perform high-accuracy DA conversion without causing deterioration in conversion accuracy due to manufacturing variations, and can prevent an increase in circuit scale and current consumption. Is to provide a device.

In order to solve the above-described problems, a DA converter according to the present invention includes any one of a resistor circuit including a plurality of resistor elements, first and second reference voltage terminals, an analog signal output terminal, and the resistor circuit. A first connection circuit that selectively connects the first reference voltage terminal to a node of the second connection circuit, and a second connection circuit that selectively connects the second reference voltage terminal to any node of the resistance circuit. And a value of a digital signal to be converted from digital to analog in a path from the node to which the first reference voltage terminal is connected to the node to which the second reference voltage terminal is connected in the resistor circuit. And a third connection circuit for selectively connecting the analog signal output terminal to any one of the corresponding nodes.

According to this configuration, the nodes of the resistor circuit to which the first reference voltage terminal and the second reference voltage terminal are connected are respectively changed by the first and second connection circuits, and the third connection circuit is correspondingly changed. As a result, the node of the resistor circuit to which the analog signal output terminal is connected is changed, so that highly accurate DA conversion can be performed without causing deterioration in conversion accuracy due to manufacturing variations. In addition, although the first, second, and third connection circuits are required, a DEM circuit such as a resistive DA converter and a current compensation circuit are unnecessary, and an increase in circuit scale and current consumption can be prevented.

In the DA converter configured as described above, the resistor circuit is a ring resistor circuit composed of a plurality of resistor elements connected in a ring shape, and the connection between the resistor elements is selected at any node of the ring resistor circuit. It is preferable to provide an open circuit that opens automatically.

According to this configuration, a plurality of resistance elements are connected in a ring shape to form a ring-shaped resistance circuit, and the first reference voltage terminal and the second reference voltage terminal are connected by the first and second connection circuits. Each node of the ring-shaped resistor circuit is changed, and the node of the ring-shaped resistor circuit to which the analog signal output terminal is connected is changed by the third connection circuit, and any of the ring-shaped resistor circuits is changed by the open circuit. Since the connection between the resistive elements is released at the position of the node, high-accuracy DA conversion can be performed without causing deterioration in conversion accuracy due to manufacturing variations. In addition, although the first, second and third connection circuits and an open circuit are required, a DEM circuit such as a resistive DA converter and a current compensation circuit are not required, and an increase in circuit scale and current consumption can be prevented. Can do.

Further, in the DA converter having an open circuit, the nodes of the ring resistance circuit to which the first reference voltage terminal and the second reference voltage terminal are connected are changed by the first and second connection circuits, respectively. Correspondingly, the node of the ring-shaped resistor circuit to which the output terminal is connected is changed by the third connection circuit, and the first reference is changed from the node to which the second reference voltage terminal is connected in the ring-shaped resistor circuit by the open circuit. It is preferable that the connection between the resistive elements is opened at the position of any node in the path returning to the node to which the voltage terminal is connected.

According to this configuration, a plurality of resistance elements are connected in a ring shape to form a ring-shaped resistance circuit, and the first reference voltage terminal and the second reference voltage terminal are connected by the first and second connection circuits. The node of the ring-shaped resistor circuit is changed, and the node of the ring-shaped resistor circuit to which the analog signal output terminal is connected is changed by the third connection circuit correspondingly, and the node in the ring-shaped resistor circuit is changed by the open circuit, Since the connection between the resistive elements is released at the position of any node in the path from the node to which the second reference voltage terminal is connected to the node to which the first reference voltage terminal is connected, conversion due to manufacturing variations High-precision DA conversion can be performed without causing a decrease in accuracy. In addition, although the first, second and third connection circuits and an open circuit are required, a DEM circuit such as a resistive DA converter and a current compensation circuit are not required, and an increase in circuit scale and current consumption can be prevented. Can do.

In the DA converter having the above-described configuration, the first connection circuit includes a first switch group connected between each node of the ring-shaped resistor circuit and the first reference voltage terminal. The circuit includes a second switch group connected between each node of the ring resistance circuit and the second reference voltage terminal, and the third connection circuit includes each node of the ring resistance circuit and an analog signal. The open circuit is composed of a fourth switch group inserted between adjacent resistor elements in the ring-shaped resistor circuit, and is connected to the first output terminal. The connection circuit is connected to each node of the ring-shaped resistor circuit on one end side of each switch of the fourth switch group, and the second and third connection circuits are the other end side of each switch of the fourth switch group. With ring resistance times The switches constituting the first, second, third and fourth switch groups are preferably switched between a short-circuit state and an open state in accordance with a digital signal to be converted. .

In the DA converter having the above configuration, in the ring-shaped resistor circuit, the node to which the first reference voltage terminal is connected, the node to which the second reference voltage terminal is connected, the node to which the analog signal output terminal is connected, and the resistor It is preferable to cycle between the nodes where the elements are opened.

In the ring-shaped resistor circuit, a node to which the first reference voltage terminal is connected, a node to which the second reference voltage terminal is connected, a node to which the analog signal output terminal is connected, and a node in which the resistor element is opened In the configuration in which the above and the like are circulated, it is preferable to perform the lap as follows, for example. That is, when a digital signal to be converted into digital-analog is input in time series, a ring-shaped resistor circuit connected to the analog signal output terminal corresponding to the value of the digital signal at the time of the previous digital-analog conversion It is preferable to perform a circulation in which one of the first and second reference voltage terminals is connected to this node during the current analog-digital conversion.

Further, as described above, when the node connected to the first reference voltage terminal and the node connected to the second reference voltage terminal are circulated, the first and second references in the ring resistance circuit As viewed from the node to which one of the voltage terminals is connected, the node having the maximum resistance value between the two nodes connected to the first and second reference voltage terminals is designated as the first and second reference voltage terminals. It is preferable that either one of the nodes is connected.

Further, as described above, when the node connected to the first reference voltage terminal and the node connected to the second reference voltage terminal are circulated as described above, in the ring-shaped resistor circuit, the resistance is set by the fourth switch group. The open end of the resistance element on one side of the node where the element is opened is a node to which the first reference voltage terminal is connected, and the open end of the resistor element on the other side of the node where the element is opened is the second. The reference voltage terminal may be connected to a node.

A delta sigma type DA converter according to the present invention is a delta sigma type digital-analog converter that converts a first digital signal sampled at a predetermined sampling frequency into an analog signal, and interpolates the first digital signal. A digital interpolation filter that converts the second digital signal to a second digital signal having a frequency higher than the sampling frequency, and a delta-sigma modulator that noise-shapes the second digital signal and converts the second digital signal to a third digital signal having a lower bit number; And a digital-analog converter for converting the third digital signal into an analog signal.

The digital-analog converter includes a ring-shaped resistor circuit composed of a plurality of resistor elements connected in a ring shape, first and second reference voltage terminals, an analog signal output terminal, and a ring-shaped resistor circuit. A first connection circuit that selectively connects the first reference voltage terminal to any node, and a second connection that selectively connects the second reference voltage terminal to any node of the ring-shaped resistance circuit In the circuit and the ring-shaped resistor circuit, the value of the digital signal to be converted from digital to analog in the path from the node connected to the first reference voltage terminal to the node connected to the second reference voltage terminal A third connection circuit that selectively connects an analog signal output terminal to one of the corresponding nodes, and an opening that selectively opens the connection between the resistance elements at the position of one of the nodes of the ring resistance circuit. Each of the nodes of the ring-like resistor circuit to which the first reference voltage terminal and the second reference voltage terminal are connected by the first and second connection circuits, respectively, and a third connection corresponding thereto The node of the ring resistance circuit to which the analog signal output terminal is connected is changed by the circuit, and the first reference voltage terminal is connected from the node to which the second reference voltage terminal is connected in the ring resistance circuit by the open circuit. The connection between the resistive elements is released at the position of any node in the path returning to the node.

According to this configuration, the same effects as the DA converter of the present invention are exhibited.

In the delta-sigma type DA converter having the above-described configuration, the first connection circuit includes a first switch group connected between each node of the ring-shaped resistance circuit and the first reference voltage terminal. The second connection circuit includes a second switch group connected between each node of the ring-shaped resistor circuit and the second reference voltage terminal, and the third connection circuit includes each node of the ring-shaped resistor circuit. And the analog signal output terminal, respectively, and the open circuit is composed of a fourth switch group inserted between the adjacent resistance elements in the ring-shaped resistance circuit. The first connection circuit is connected to each node of the ring-shaped resistance circuit on one end side of each switch of the fourth switch group, and the second and third connection circuits are connected to each switch of the fourth switch group. The other end side Each of the switches constituting the first, second, third and fourth switch groups connected to each node of the ring resistance circuit is switched between a short-circuit state and an open state according to a digital signal to be converted. It is preferred that

In the delta-sigma type DA converter having the above configuration, the decoder preferably switches the first, second, third, and fourth switch groups so as to randomize the influence due to the manufacturing variation.

In the delta-sigma type DA converter having the above configuration, the decoder preferably switches the first, second, third, and fourth switch groups so that the same switch group is not always selected.

According to the DA converter of the present invention, a plurality of resistance elements are connected in a ring shape to form a ring-shaped resistance circuit, and the first reference voltage terminal and the second reference voltage are configured by the first and second connection circuits. The node of the ring-shaped resistor circuit to which the voltage terminal is connected is changed, and the node of the ring-shaped resistor circuit to which the analog signal output terminal is connected is changed by the third connection circuit, and the ring shape is changed by the open circuit. In the resistor circuit, since the connection between the resistive elements is released at the position of any node in the path returning from the node to which the second reference voltage terminal is connected to the node to which the first reference voltage terminal is connected, High-accuracy DA conversion can be performed without causing deterioration in conversion accuracy due to manufacturing variations. In addition, although the first, second, and third connection circuits are required, a DEM circuit such as a resistive DA converter and a current compensation circuit are unnecessary, and an increase in circuit scale and current consumption can be prevented.

Further, according to the delta-sigma type DA converter of the present invention, since it is configured using the above-described DA converter of the present invention, the same effects as the DA converter of the present invention are exhibited.

FIG. 1 is a circuit diagram showing a configuration of a DA converter according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a DA converter configured using the DA converter according to the first embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a delta-sigma type DA converter according to Embodiment 2 of the present invention configured using the DA converter of the present invention. FIG. 4 is a circuit diagram showing a configuration of a general resistor string type DA converter. FIG. 5 is a circuit diagram showing a configuration of a general resistance type DA converter. FIG. 6 is a block diagram showing a configuration of a general delta-sigma type DA converter. FIG. 7 is a block diagram showing a configuration of a delta-sigma type conversion device to which a DEM circuit and a current compensation circuit are added.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
DA converter of the first embodiment of the present invention, as shown in FIG. 1, a plurality of resistive elements connected in a ring R _1, R _2, · · ·, a ring-shaped resistor circuit 1 consisting of R _N , First and second reference voltage terminals V _ref1 , V _ref2 , analog signal output terminal V _out, and any one of the nodes of the ring resistance circuit 1 (resistance elements R ₁ , R ₂ ,..., R _A first connection circuit 2 that selectively connects the first reference voltage terminal V _ref1 to the connection point between _N and a second reference voltage terminal V _ref2 that is selected at any node of the ring-shaped resistance circuit 1 In the second connection circuit 3 and the ring resistance circuit 1 in the path from the node to which the first reference voltage terminal V _ref1 is connected to the node to which the second reference voltage terminal V _ref2 is connected Any of the nos corresponding to the value of the digital signal to be converted from digital to analog In a third connecting circuit 4 for selectively connecting the analog signal output terminal V _out, the resistance element R ₁ at the position of any node of the ring-shaped resistor circuit 1, R _2, ···, between R _N And an open circuit 5 for selectively releasing the connection.

In this DA converter, the nodes of the ring-shaped resistance circuit 1 to which the first reference voltage terminal V _ref1 and the second reference voltage terminal V _ref2 are connected by the first and second connection circuits 2 and 3 respectively. Any node in the path changed and returned from the node connected to the second reference voltage terminal V _ref2 to the node connected to the first reference voltage terminal V _ref1 in the ring-shaped resistance circuit 1 by the open circuit 5 Of the ring-shaped resistance circuit 1 in which the connection between the resistance elements R ₁ , R ₂ ,..., R _N is opened and the analog signal output terminal V _out is correspondingly connected by the third connection circuit. The node is changed.

In the DA converter configured as described above, the first connection circuit 2 includes a first switch group (switch S) connected between each node of the ring-shaped resistor circuit 1 and the first reference voltage terminal V _{ref1. d_1} , S _{d_2} ,..., S _{d_N} ). The second connection circuit 3 includes a second switch group (switches S _{g_1} , S _{g_2} ,...) Connected between each node of the ring resistance circuit 1 and the second reference voltage terminal V _ref2 . _{Sg_N} ). Third connection circuit 4, a third switch group that is connected between each node and the analog signal output terminal V _out of _the ring-shaped resistor circuit 1 (switch _{S o_1, S o_2, ···,} S o_N Consist of). Open circuit 5, the ring-shaped resistor circuit 1, the resistance element R ₁ adjacent, R _2, · · ·, a fourth group of switches respectively inserted between the adjacent R _N (switch S _{r_1,} S _{r_2,} · _··· , _{Sr_N} ).

The first connection circuit 2 is connected to each node of the ring-shaped resistance circuit 1 on one end side of each switch S _{r_1} , S _{r_2} ,..., S _{r_N} of the fourth switch group serving as the open circuit 5. The second and third connection circuits 3 and 4 are connected to each of the ring-shaped resistance circuits 1 on the other end side of the switches S _{r_1} , S _{r_2 ,.} Connected to the node. And each switch which comprises the 1st, 2nd, 3rd and 4th switch group is switched to a short circuit state and an open state according to the digital signal used as conversion object.

In the DA converter configured as described above, in the ring-shaped resistor circuit 1, a node to which the first reference voltage terminal V _ref1 is connected, a node to which the second reference voltage terminal V _ref2 is connected, and an analog signal output terminal. The node to which V _out is connected and the node in which the resistance elements R ₁ , R ₂ ,..., R _N are opened are circulated each time DA conversion of one digital signal is performed.

The patrol is performed as follows, for example. That is, when digital signals to be converted into digital-analog are input in time series, a ring connected to the analog signal output terminal _Vout corresponding to the value of the digital signal at the previous digital-analog conversion. A cycle is performed in which the node of the resistor circuit 1 is used as a node to which one of the first and second reference voltage terminals V _ref1 and V _ref2 is connected during the current analog-digital conversion.

Further, as described above, in the case where the node connected to the first reference voltage terminal V _ref1 and the node connected to the second reference voltage terminal V _ref2 are circulated, and when viewed from any node one is connected to the second reference voltage terminal V _ref1, V _ref2, the resistance value between both nodes connected to the first and second reference voltage terminals V _ref1, V _ref2 is The maximum node is a node to which the other of the first and second reference voltage terminals V _ref1 and V _ref2 is connected.

Further, as described above, when the node connected to the first reference voltage terminal V _ref1 and the node connected to the second reference voltage terminal V _ref2 are circulated, the ring-shaped resistor circuit 1 has an open circuit. Any one of the nodes in which the resistance elements R ₁ , R ₂ ,..., R _N are opened by a fourth switch group (consisting of switches S _{r_1} , S _{r_2 ,.} The open end of the resistor element on one side is a node to which the first reference voltage terminal V _ref1 is connected, and the open end of the resistor element on the other side of the node where the resistor elements are open is the second reference voltage terminal V. It is a node to which _ref2 is connected.

Hereinafter, the DA converter according to the first embodiment will be described in more detail. This DA converter has a reference voltage terminal V _{ref1 to which} a high voltage is supplied, a reference voltage terminal V _ref2 to which a low voltage is supplied, and the same resistance value R in a number corresponding to the necessary resolution for DA conversion. resistive element group having (ring-shaped (resistor connected in a loop) element R _1, R _2, · · ·, consists R _N) and the reference voltage terminal V _ref1 and the resistor element group and a switch group that connects ( switch S _{d_1,} S _{d_2,} · · ·, consists S _{d_n)} and the reference voltage terminal V _ref2 and the resistor element group and a switch group that connects (switch S _{g_1,} S _{g_2,} · · ·, consists S _{G - n)} When the resistance element R ₁ connected in a ring, R _2, · · ·, each inserted switches between the adjacent resistive elements adjacent to each other in R _N (switch S _{r_1,} S _{r_2,} · · ·, and S consists of _{R_n),} to connect the analog signal output terminal V _out and the resistive element group The switch group consisting of (switch _S o_1, S o_2, ···, consisting of _S o_N) and.

In the case of the (N−1) value DA converter, there are N resistance elements and respective switches. The k-th resistance element R _k has one terminal connected to the k-th switches S _{g_k} , S _{r_k} , S _{o_k} , and the other terminal connected to the (k + 1) -th switches S _{d_k + 1} , S _{r_k + 1} . Has been. The k-th switch S _{d_k} has one terminal connected to the reference voltage terminal V _ref1 and the other terminal connected to the (k−1) -th resistance element R _k-1 and the k-th switch S _{r_k.} Yes. The k-th switch S _{g_k} has one terminal connected to the reference voltage terminal V _ref2 and the other terminal connected to the k-th resistance element R _k and the k-th switches S _{r_k} and _{So_k} . The kth switch S _{r_k} has one terminal connected to the (k−1) th resistor element R _k−1 and the kth switch S _{d_k,} and the other terminal connected to the kth resistor element R _k . The kth switches S _{g_k} and S _{o_k} are connected. The k-th switch S _{o_k} has one terminal connected to the k-th resistance element R _k and the k-th switches S _{r_k} and S _{g_k,} and the other terminal connected to the analog signal output terminal V _out . .

DA converter of the first embodiment of the present invention, each of the switches _{S d_1, S d_2, ···,} S d_N, S g_1, S g_2, ···, S g_N, S r_1, S r_2, ··· , S _{r_N} , S _{o_1} , S _{o_2} ,..., S _{o_N} , the voltages at the reference voltage terminal V _ref1 and the reference voltage terminal V _ref2 are the same as in the resistor string DA converter shown in FIG. A voltage obtained by dividing the difference by (N−1) can be obtained.

Switch S _{d_1} to obtain this _{voltage, S d_2, ···, S d_N} , S g_1, S g_2, ···, S g_N, S r_1, S r_2, ···, S r_N, S o_1, S The control of _{o_2} ,..., S _{o_N} will be described below.

Now, in the switch group connecting the reference voltage terminal V _ref1 and the resistor element group, the k-th switch S _{d_k} is short-circuited, and the other N−1 switches S _{d_1} , S _{d_2} ,..., S _{d_k− 1} , S _{d_k + 1} ,..., S _{d_N} are open, and in the switch group connecting the reference voltage terminal V _ref2 and the resistance element group, the kth switch S _{g_k} is short-circuited, and the other N− one switch _{S g_1, S g_2, ···,} S g_k-1, S g_k + 1, ···, and _S g_N is open. At this time, in the switch group connecting the resistance elements, the k-th switch S _{r_k} is opened, and the other N−1 switches S _{r_1} , S _{r_2} ,..., S _{r_k−1} , S _{r_k + 1.} ..., _{Sr_N} are short-circuited.

In the DA converter of the present invention, when taking out a voltage corresponding to the voltage between the conventional resistor string type DA converter shown in FIG. 4, the resistance element R _l-1 and the resistance element R _l are, (k + l ) _Divided by N is m, the m-th switch S _{o_m} of the switch group connecting the analog signal output terminal V _out and the resistance element group is short-circuited, and the other N−1 switches S _{o_1} , S _{o_2} ,..., S _{o_m −1} , S _{o_m + 1 ,.}

By thus controlling the switches, in the DA converter of the first embodiment, the resistance element R _N resistive elements R _k-1 connected to the switch S _{d_k} is of a conventional resistor string type DA converter , the resistor R ₁ resistive element R _k which are connected to the switch S _{G_k} is of a conventional resistor string type DA converter, the resistance element is connected to a switch _{S o_m R m-1, R} m is the conventional, respectively resistance in the resistor string type DA converter element R _l-1, corresponds to R _l, can be taken out a desired voltage.

Thus constituted result, the DA converter of the first embodiment of the present invention shown in FIG. 1, the reference voltage terminal V _ref1 and the resistor element group (resistive element R _1, R _2, · · ·, consists R _N ) switches for connecting the (switch S _{d_1,} S _{d_2,} ···, consists S _{d_n),} the reference voltage terminal V _ref2 and the resistor element group (resistive element R _1, R _2, ···, from R _N becomes) a switch group that connects (switch S _{g_1,} S _{g_2,} ···, consists S _{G - n),} resistive element group (resistive element R _1, R _2, ···, consists R _N) adjacent the A group of switches (consisting of switches S _{r_1} , S _{r_2} ,..., S _{r_N} ) that connect the resistance elements, and an analog signal output terminal V _out and a group of resistance elements (resistance elements R ₁ , R ₂ ,... , switches for connecting the consisting R _N) (switch _S o_1, S o_2, ···, consists _S o_N) Therefore, the two reference voltage terminals V _ref1, V _ref2, resistive element group for performing the DA conversion by partial pressure is cyclically the connection point of the (resistive element R _1, R _2, · · ·, consists R _N) Thus, the effects of manufacturing variations can be randomized. Further, since the DA converter according to the first embodiment of the present invention performs DA conversion based on the same operation principle as that of the resistor string type DA converter, the current value does not change due to the influence of the resistance component of the reference voltage terminal. .

As described above, according to the first embodiment, a plurality of resistance elements R _1, R _2, · · ·, by connecting R _N in a ring shape and a ring-shaped resistor circuit 1, the first and The nodes of the ring-shaped resistor circuit 1 to which the first reference voltage terminal V _ref1 and the second reference voltage terminal V _ref2 are connected are changed by the second connection circuits 2 and 3, respectively. Since the node at which the connection is released is changed, and the node of the ring-shaped resistor circuit 1 to which the analog signal output terminal _Vout is connected is changed by the third connection circuit 4 correspondingly, the conversion accuracy due to manufacturing variations is improved. High-precision DA conversion can be performed without causing a decrease. In addition, although the first, second and third connection circuits 2, 3, 4 and the open circuit 5 are added, a DEM circuit such as a resistive DA converter and a current compensation circuit are unnecessary, and the circuit scale is An increase in current consumption can also be prevented.

That is, the DA converter according to the first embodiment of the present invention can randomize the influence due to the manufacturing variation like the DEM, and can reduce the increase of the integral nonlinearity error and the deterioration of the distortion. Further, there is no change in current value due to digital data input, and an increase in circuit scale and current consumption due to insertion of a current compensation circuit can be prevented.

As a specific embodiment of the present invention, the operation of a DA converter as shown in FIG. 2 that performs 7-value DA conversion will be described. In the embodiment of FIG. 2, the digital input Din, specifically, the 3-bit digital signals D ₁ , D ₂ and D ₃ are converted into control signals for the respective switches for driving the DA converter shown in FIG. 1 and the DA converter 70 shown in FIG. An analog output Aout is output from the DA converter 70.

The decoder 60 receives 3-bit digital signals D ₁ , D ₂ , D ₃ as input, and receives eight digital signals D _{v_1} , D _{v_2} ,..., D _{v_8} and eight digital signals D _{r_1} , D _{r_2 ,. ..} , D _{r_8} and eight digital signals D _{o_1} , D _{o_2} ,..., D _{o_8} are output.

Digital signal _{D v_1, D v_2, ···,} D v_8 , in the DA converter 70, the reference voltage terminal V _ref1, V _ref2 and the resistor element group (resistive element _{R 1, R 2, ···,} R N switch group that connects from the consisting) (switch S _{d_1,} S _{d_2,} using · · ·, S consists _{D_8)} and switch group (switches S _{g_1,} S _{g_2,} ···, as a control signal consisting of S _{G_8)} It is done.

The digital signals D _{r_1} , D _{r_2} ,..., D _{r_8} are control signals for a switch group (consisting of switches S _{r_1} , S _{r_2} ,..., S _{r_8} ) connecting the resistance elements in the DA converter 70. Used as

Digital signals D _{o_1} , D _{o_2} ,..., D _{o_8} control the switch group ( _{consisting of} switches S _{o_1} , S _{o_2} ,..., S _{o_8} ) that connects the analog signal output terminal V _out and the resistor element group. Used as a signal.

The decoder 60 decodes the digital input signal with a certain rule, and outputs a digital signal so that the same switch is not always selected.

As a decoder input, for example, digital signals “011”, “110”, “100”, “011”, “101”, “011”, “100”, “010”, “001”, “110” are consecutive. Then, consider the case of conversion.

Now, the decoder 60 _reads “When D _{o_k} = 1 in the previous conversion, D _{v_k} = 1 in the current conversion, and when D _{o_l} = 0 in the previous conversion, D _{v_l} = Suppose that it has a conversion law of “0”. For simplicity, regarding the two reference voltage terminals V _ref1 and V _ref2 of the DA converter 70, the voltage of the reference voltage terminal V _ref1 is 1 and the voltage of the reference voltage terminal V _ref2 is 0. Table 1 shows the digital output of the decoder 60 and the analog output of the DA converter 70 at this time.

The digital signals D _{v_1} , D _{v_2} ,..., D _{v_8} use the digital signals D _{o_1} , D _{o_2} , ..., D _{o_8} of the previous conversion as they are, and the digital signals D _{r_1} , D _{r_2} , _.. , D _{r_8} is _obtained by inverting the digital signals D _{v_1} , D _{v_2,.} The digital signals D _{o_1} , D _{o_2} ,..., D _{o_8} are converted to a desired analog output determined by the digital signals D ₁ , D ₂ , and D ₃ input to the decoder 60, It is decided in the same way.

Simply put, this cyclic method uses the number of the switch used to connect the analog signal output terminal _Vout and the resistive element group in the previous conversion, and the two reference voltage terminals _Vref1 , Vref in the next conversion. The number of the switch that connects _ref2 and the resistive element group is the same, and the switch that connects the resistive elements is controlled in the reverse manner to the switch that connects the two reference voltage terminals and the resistive element group. ,realizable.

As described above, by using the DA converter according to the first embodiment of the present invention, the switches S _{d_1} , S _{d_2} ,..., S _{d_N} , the reference voltage terminal connecting the reference voltage terminal V _ref1 and the resistor element group. switch S _{g_1} connecting a resistive element group and _{V ref2, S g_2, ···,} S g_N, switch S _{O_1} for connecting the analog signal output terminal V _out resistance element _group, S o_2, ···, the S _{O_N} While circulating, an analog signal can be taken out by the same mechanism as the resistor string DA converter. In other words, in the present invention, in a plurality of resistance elements connected in a ring shape, DA conversion is performed by a mechanism similar to that of a resistance string type DA converter by circulating a connection point between two reference voltage terminals V _ref1 and V _ref2. I do. As a result, the effects of manufacturing variations can be randomized, integration nonlinearity can be increased, distortion can be reduced, and there is no change in the current value due to digital data input. An increase in current consumption can also be prevented.

The above-described DA converter can also be used as a 9-value DA converter by directly outputting the voltages of the reference voltage terminals V _ref1 and V _ref2 . In the above description, the 7-value DA conversion is shown as an example, but the DA conversion may have any resolution. In addition to the cyclic method shown in the embodiment, a number of decoder controls can be considered. For example, as described in Patent Document 3, what is written in a document related to DEM can be applied.

In the above-described embodiment, the node that opens the connection between the resistive elements and the node that is connected to the first and second reference voltage terminals are the same node, but it is not necessary to be the same node. That is, at least one of the first and second reference voltage terminals may be connected to a node other than both ends of the series circuit of all the resistive elements in the resistive element group. In this case, the resistance element located outside the node to which the first and second reference voltage terminals are connected does not contribute to DA conversion.

In the above embodiment, any node of the ring-shaped resistor circuit 1 is selectively opened by the open circuit 5, but the resistor circuit is constituted by a series circuit of a plurality of resistors, An example in which is omitted can be given as an example. This configuration is equivalent to a fixed open node in the ring resistance circuit.

(Embodiment 2)
Next, a delta-sigma type DA converter according to Embodiment 2 using the DA converter of the present invention will be described with reference to FIG. The delta sigma type DA converter in FIG. 3 is a delta sigma type DA converter that converts a first digital signal sampled at a predetermined sampling frequency into an analog signal. A digital interpolation filter 80 that interpolates Din and converts it to a second digital signal having a frequency higher than the sampling frequency, and noise-shapes the second digital signal to convert it to a third digital signal having a lower bit number. The delta-sigma modulator 90, the decoder 100 that decodes the third digital signal output from the delta-sigma modulator 90, and the third digital signal is converted into an analog signal, that is, an analog output Aout using the output of the decoder 100 as a drive signal. The DA converter 110 is provided. As the decoder 100 and the digital-analog converter 110, those described in the first embodiment are used.

The digital interpolation filter 80 has the same configuration as that shown in FIGS. 7 and 8, and a digital signal having an oversampling frequency f _os while preventing aliasing with respect to a digital input signal having a certain sampling frequency f _s and n bits. Is output. The oversampling frequency f _os depends on the oversampling rate OSR. F _os = OSR × f _s
Have a relationship. The oversampling frequency f _os, generally 64f _s, the frequency of such 128f _s used.

The delta sigma modulator 90 converts the data obtained from the digital interpolation filter 80 into lower resolution data at a frequency higher than the sampling frequency f _s with the same configuration as that shown in FIGS. 7 and 8. At the same time, noise shaping is performed. Further, the decoder 100 converts the high-frequency, low-resolution data obtained from the delta-sigma modulator 90 into a digital signal for driving the DA converter 110 of the present invention by the decoder 100. The DA converter 110 of the present invention Based on the output of the decoder 100, an analog signal corresponding to the high-frequency, low-resolution data obtained from the delta-sigma modulator 90 is output.

According to the second embodiment, as described in the first embodiment, since this DA converter can reduce deterioration of conversion error due to manufacturing variations and current value changes, the delta sigma type DA converter is provided with this DA converter. By using the DA converter, high-accuracy DA conversion can be performed without causing deterioration in conversion accuracy due to manufacturing variations. In addition, since a current compensation circuit is unnecessary, an increase in circuit scale and current consumption can be prevented.

The DA converter and the delta-sigma modulation type DA converter according to the present invention can reduce the deterioration of the conversion error due to the manufacturing variation and the change of the current value, and the high-precision DA conversion without causing the deterioration of the conversion accuracy due to the manufacturing variation. In addition, since the current compensation circuit is unnecessary, the circuit scale and current consumption can be prevented from increasing, which is useful as a DA conversion processing circuit in a digital music player or the like.

_{DESCRIPTION OF SYMBOLS} 1 Ring-shaped resistance circuit 2 1st connection circuit 3 2nd connection circuit 4 3rd connection circuit 5 Open circuit 80 Digital interpolation filter 90 Delta-sigma modulator 100 Decoder 110 DA converter V _ref1 1st reference voltage terminal V _ref2 second reference voltage terminal _{R 1, R 2, ···,} R N resistive elements _{S d_1, S d_2, ···,} S d_N switch _{S g_1, S g_2, ···,} S g_N switch S _{O_1,} S _{o_2} , ..., S _{o_N} switch S _{r_1} , S _{r_2} , ..., S _{r_N} switch

Claims (12)

1. A resistance circuit composed of a plurality of resistance elements;
   First and second reference voltage terminals;
   An analog signal output terminal;
   A first connection circuit that selectively connects the first reference voltage terminal to any node of the resistance circuit;
   A second connection circuit for selectively connecting the second reference voltage terminal to any node of the resistance circuit;
   Corresponding to the value of the digital signal to be converted from digital to analog in the path from the node to which the first reference voltage terminal is connected to the node to which the second reference voltage terminal is connected in the resistor circuit And a third connection circuit for selectively connecting the analog signal output terminal to any one of the nodes.
2. The resistor circuit is a ring resistor circuit composed of a plurality of resistor elements connected in a ring shape, and an open circuit that selectively opens a connection between the resistor elements at any node of the ring resistor circuit. The digital-analog converter according to claim 1, further comprising:
3. The nodes of the ring-shaped resistance circuit to which the first reference voltage terminal and the second reference voltage terminal are connected are respectively changed by the first and second connection circuits, and the third connection is correspondingly changed. The node of the ring-shaped resistor circuit to which the output terminal is connected is changed by a circuit, and the first reference voltage from the node to which the second reference voltage terminal is connected in the ring-shaped resistor circuit by the open circuit 3. The digital-analog converter according to claim 2, wherein the connection between the resistive elements is opened at the position of any node in the path returning to the node to which the terminal is connected.
4. The first connection circuit includes a first switch group connected between each node of the ring resistance circuit and the first reference voltage terminal,
   The second connection circuit includes a second switch group connected between each node of the ring resistance circuit and the second reference voltage terminal,
   The third connection circuit includes a third switch group connected between each node of the ring resistance circuit and the analog signal output terminal,
   The open circuit comprises a fourth switch group inserted between adjacent resistance elements in the ring resistance circuit,
   The first connection circuit is connected to each node of the ring resistance circuit on one end side of each switch of the fourth switch group,
   The second and third connection circuits are connected to each node of the ring resistance circuit on the other end side of each switch of the fourth switch group,
   4. The digital-analog device according to claim 3, wherein each of the switches constituting the first, second, third, and fourth switch groups is switched between a short circuit state and an open state according to the digital signal to be converted. converter.
5. In the ring-shaped resistance circuit, a node between the first reference voltage terminal, a node to which the second reference voltage terminal is connected, a node to which the analog signal output terminal is connected, and a resistance element are opened. 4. The digital-analog converter according to claim 3, wherein each of the nodes is circulated.
6. The digital signal to be converted into digital to analog is input in time series, and the node of the ring-shaped resistance circuit connected to the analog signal output terminal corresponding to the value of the digital signal at the time of the previous digital to analog conversion 6. The digital-analog converter according to claim 5, wherein at least one of the first and second reference voltage terminals is connected at the time of the current analog-digital conversion.
7. In the ring resistance circuit, when viewed from a node to which one of the first and second reference voltage terminals is connected, a resistance value between both nodes connected to the first and second reference voltage terminals 7. The digital-analog converter according to claim 5, wherein a node having the largest value is a node to which one of the first and second reference voltage terminals is connected.
8. In the ring-shaped resistor circuit, an open end of a resistor element on one side of a node where the resistor element is opened by the fourth switch group is a node to which the first reference voltage terminal is connected, and the resistor element is connected. 7. The digital-analog converter according to claim 5, wherein the open end of the resistance element on the other side of the node where the second reference voltage terminal is connected is a node to which the second reference voltage terminal is connected.
9. A delta-sigma type digital-analog conversion device for converting a first digital signal sampled at a predetermined sampling frequency into an analog signal,
   A digital interpolation filter that interpolates the first digital signal and converts it to a second digital signal having a frequency higher than the sampling frequency;
   A delta-sigma modulator that noise-shapes the second digital signal to convert it to a third digital signal having a lower number of bits;
   A digital-analog converter for converting the third digital signal into the analog signal;
   The digital-analog converter is:
   A ring-shaped resistance circuit composed of a plurality of resistance elements connected in a ring shape;
   First and second reference voltage terminals;
   An analog signal output terminal;
   A first connection circuit that selectively connects the first reference voltage terminal to any node of the ring-shaped resistance circuit;
   A second connection circuit for selectively connecting the second reference voltage terminal to any node of the ring resistance circuit;
   In the ring-shaped resistance circuit, the value of the digital signal to be converted into digital to analog in the path from the node to which the first reference voltage terminal is connected to the node to which the second reference voltage terminal is connected. A third connection circuit for selectively connecting the analog signal output terminal to one of the corresponding nodes;
   An open circuit that selectively opens the connection between the resistive elements at the position of any node of the ring-shaped resistance circuit,
   The nodes of the ring-shaped resistance circuit to which the first reference voltage terminal and the second reference voltage terminal are connected are respectively changed by the first and second connection circuits, and the third connection is correspondingly changed. A node of the ring-shaped resistor circuit to which the analog signal output terminal is connected is changed by a circuit, and the first reference voltage terminal is connected to the first resistor in the ring-shaped resistor circuit by the open circuit. A delta-sigma type digital-analog converter characterized in that a connection between resistive elements is opened at a position of any node in a path returning to a node to which a reference voltage terminal is connected.
10. The first connection circuit includes a first switch group connected between each node of the ring resistance circuit and the first reference voltage terminal,
    The second connection circuit includes a second switch group connected between each node of the ring resistance circuit and the second reference voltage terminal,
    The third connection circuit includes a third switch group connected between each node of the ring resistance circuit and the analog signal output terminal,
    The open circuit comprises a fourth switch group inserted between adjacent resistance elements in the ring resistance circuit,
    The first connection circuit is connected to each node of the ring resistance circuit on one end side of each switch of the fourth switch group,
    The second and third connection circuits are connected to each node of the ring resistance circuit on the other end side of each switch of the fourth switch group,
    The delta-sigma type switch according to claim 9, wherein each of the switches constituting the first, second, third, and fourth switch groups is switched between a short-circuit state and an open state according to the digital signal to be converted. Digital-analog converter.
11. 11. The delta sigma type digital-analog conversion device according to claim 10, wherein the decoder switches the first, second, third and fourth switch groups so as to randomize the influence due to manufacturing variation.
12. 11. The delta-sigma type digital-analog conversion device according to claim 10, wherein the decoder switches the first, second, third and fourth switch groups so that the same switch group is not always selected.

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